Semiconductor chip fabrication is a complicated process that involves a coordinated series of precise operations. It is well known that during the various steps in these operations, the surfaces, edges, and bevels of the semiconductor substrate (i.e., semiconductor wafers) become contaminated with a layer of residue comprised of particulates, organic materials, metallic impurities (e.g., copper, aluminum, titanium, tungsten, etc.), and native oxides (e.g., silicon dioxide, etc.). The removal of these contaminants is a priority to semiconductor chip fabricators because the level of contamination on the wafer inversely correlates to the integrated circuit (IC) chip yield for each wafer and the overall reliability of those IC chips. Some examples of operations that may result in unwanted wafer contamination include plasma etching, chemical mechanical polishing (CMP), chemical vapor deposition (CVD), and metallization (e.g., copper electroplating, sputtering, etc.).
Increasingly, IC chip manufacturers are beginning to require removal of contaminants from the edge and bevel surfaces (i.e., bevel edge surfaces) of the semiconductor wafer. Their motivation is to increase each wafer's IC chip yield by reducing defects caused by bevel-edge borne contaminants that may flake off during the IC fabrication process and cross-contaminate wafers within a batch, or in other batches. Examples of conventional methods used to remove residue from the bevel edge surface of the wafer include chemical immersion of the entire wafer and direct application of chemicals to the surface of the wafer (i.e. clean the bevel edge while performing a standard immersion clean in a wet bench). Another method is to place the wafer face-down on a Bernoulli chuck and clean the backside with reaction chemistry, also cleaning the exposed bevel edge (i.e. SEZ approach).
The chemical immersion (CI) method involves dipping the entire wafer or wafer batch into a tank of chemicals and subsequently drying the wafer using techniques such as spin rinse drying (SRD) or Marangoni drying. There are several inherent limitations and disadvantages with the CI method. The method is not effective at cleaning polymer-based residues typically found on the bevel edge surface of the wafer. Polymer-based residues tend to be chemically resistant and require highly caustic chemical cleaners (e.g., HF, etc.) to effectuate their removal. As described above, CI methods expose the entire wafer to the chemical cleaner during the cleaning process. Since highly caustic chemical cleaners damage active regions of the wafer (typically not coated with the polymer-based residue), CI methods limit the types of chemical cleaners that can be used. Therefore, CI methods cannot be effectively utilized to clean polymer-based residues on the bevel edge surface of wafer. Further, CI methods sometimes cause contaminants to be transferred from the backside of the wafers to the front side of the wafer facing opposite. This is due to the removed contaminants, floating on the surface layer of the chemical solution in CI tank, attaching to the front and back sides of the wafer as it is being removed from the tank. As for conventional direct chemical application methods, they are disadvantaged because they do not allow for precise control over the area on the wafer surface that chemical is applied to thus limiting the types of chemical cleaners that can be used. This again poses difficulties when cleaning polymer-based residues on the bevel edge surfaces of the wafer.
In view of the forgoing, there is a need for a cleaning apparatus that avoids the problems of the prior art by allowing for precise application of chemicals to the edge surface of the semiconductor wafer.